Method of reducing carbon incorporation into films produced by chemical vapor deposition involving organic precursor compounds

ABSTRACT

A chemical vapor deposition method of providing a layer of material atop a semiconductor wafer using an organic precursor includes, a) positioning a wafer within a chemical vapor deposition reactor; b) injecting an organic precursor to within the reactor having the wafer positioned therein, and maintaining the reactor at a temperature and a pressure which in combination are effective to deposit a first layer of material onto the wafer which incorporates carbon from the organic precursor; and c) after depositing the first layer, ceasing to inject the organic precursor into the reactor and injecting a component gas into the reactor and generating a plasma within the reactor against the first layer, the component gas and plasma generated therefrom having a component which is effective when in an activated state to interact with a component of the deposited first layer to remove carbon from the first layer and produce gaseous products which are expelled from the reactor. In one aspect, the component gas provides a bonding component which replaces and substitutes for the carbon displaced from carbide present in the layer. In another aspect, the &#34;b&#34; and &#34;c&#34; steps are repeated to deposit more of the same layers.

RELATED PATENT DATA

This patent resulted from a continuation-in-part application of U.S.patent application Ser. No. 08/336,260 filed on Nov. 8, 1994, now U.S.Pat. No. 5,576,071, entitled, "Method Of Reducing Carbon IncorporationInto Films Produced By Chemical Vapor Deposition Involving OrganicPrecursor Compounds", listing Gurtej S. Sandhu as the inventor.

TECHNICAL FIELD

This invention relates to methods of reducing carbon incorporation intofilms produced by chemical vapor deposition involving organometallicprecursor compounds.

BACKGROUND OF THE INVENTION

Chemical vapor deposition (CVD) is defined as the formation of anon-volatile solid film on a substrate by the reaction of vapor phasereactants that contain desired components. The gases are introduced intoa reactor vessel, and decompose and react at a heated surface on thewafer to form the desired film. Chemical vapor deposition is but oneprocess of providing thin films on semiconductor wafers, such as filmsof elemental metals or compounds. It is a favored deposition process inmany respects, principally because of its ability to provide highlyconformal layers even within deep contacts and other openings.

Organic compounds are commonly utilized as chemical vapor depositionprecursors. One subclass of this group which is finding increasing usein chemical vapor deposition of metals and metal compounds areorganometallic precursors. Specifically, an example is the reaction of atitanium organometallic precursor of the formula Ti(N(CH₃)₂)₄, namedtetrakisdimethyl-amidotitanium (TDMAT), and ammonia in the presence of acarrier gas which reacts to produce TiN according to the followingformula:

    Ti(NR.sub.2).sub.4 +NH.sub.3 →TiN+organic by-products

Organometallic compounds contain a central or linking atom or ion (Ti inTDMAT) combined by coordinate bonds with a definite number ofsurrounding ligands, groups or molecules, at least one of which isorganic (the (N(CH₃)₂ groups in TDMAT). The central or linking atom asaccepted within the art may not be a "metal" in the literal sense. Asaccepted within the art of organometallic compounds, the linking atomcould be anything other than halogens, the noble gases, H, C, N, O, P,S, Se, and Te.

The above and other chemical vapor deposition reactions involvingorganometallics are typically conducted at low pressures of less than 1Torr. It is typically desirable in low pressure chemical vapordeposition processes to operate at as low a pressure as possible toassure complete evacuation of potentially undesirable reactive andcontaminating components from the chamber. Even small amounts of thesematerials can result in a significant undesired increase in filmresistivity. For example, oxygen incorporation into the film before andafter deposition results in higher resistivity. Additionally, it isbelieved that organic incorporation (specifically pure carbon orhydrocarbon incorporation) into the resultant film reduces density andresistivity. Such organic incorporation can result from carbon radicalsfrom the organic portion of the precursor becoming incorporated into thefilm, as opposed to being expelled with the carrier gas. Carbonincorporation can also cause other undesired attributes in the depositedfilm, such as low density which causes oxygen incorporation into thefilm when exposed to ambient air.

Hydrogen is a known capable reactant with deposited carbon or metalcarbides. Such will react with carbon atoms to form volatilehydrocarbons. Hydrogen atoms, radicals or ions are more reactive thanmolecular hydrogen in producing volatile hydrocarbons.

It would be desirable to improve upon these and other prior art chemicalvapor deposition processes in producing layers having minimalincorporated carbon.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the accompanying drawings, which are briefly describedbelow.

FIG. 1 is a diagrammatic sectional view of a semiconductor wafer at oneprocessing step in accordance with the invention.

FIG. 2 is a view of the FIG. 1 wafer at a processing step subsequent tothat shown by FIG. 1.

FIG. 3 is a view of the FIG. 1 wafer shown at a processing stepsubsequent to that shown by FIG. 2.

FIG. 4 is a view of the FIG. 1 wafer shown at a processing stepsubsequent to that shown by FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws "to promote the progressof science and useful arts" (Article 1, Section 8).

In accordance with one aspect of the invention, a chemical vapordeposition method of providing a layer of material atop a semiconductorwafer using an organic precursor comprises the following steps:

positioning a wafer within a chemical vapor deposition reactor;

injecting an organic precursor to within the reactor having the waferpositioned therein, and maintaining the reactor at a temperature and apressure which in combination are effective to deposit a first layer ofmaterial onto the wafer which incorporates carbon from the organicprecursor; and

after depositing the first layer, ceasing to inject the organicprecursor into the reactor and injecting a component gas into thereactor and generating a plasma from the component gas within thereactor against the first layer, the component gas and plasma generatedtherefrom having a component which is effective when in an activatedstate to interact with a component of the deposited first layer toremove carbon from the first layer and produce gaseous products whichare expelled from the reactor.

In accordance with another aspect of the invention, a chemical vapordeposition method of providing a layer of material atop a semiconductorwafer using an organic precursor comprises the following steps:

positioning a wafer within a chemical vapor deposition reactor;

injecting an organic precursor to within the reactor having the waferpositioned therein, and maintaining the reactor at a temperature and apressure which in combination are effective to deposit a first layer ofmaterial onto the wafer which incorporates carbon from the organicprecursor in the form of a carbide; and

after depositing the first layer, ceasing to inject the organicprecursor into the reactor and injecting a component gas into thereactor and generating a plasma from the component gas within thereactor against the first layer, the component gas and plasma generatedtherefrom having a component which is effective when in an activatedstate to chemically react with a component of the deposited first layer,the activated state component effectively diffusing into the first layerto remove carbon of the carbide from the first layer and produce gaseousproducts which are expelled from the reactor, the component gasproviding a bonding component which replaces and substitutes for thecarbon displaced from the carbide in the first layer.

In another aspect, the depositions and plasma treatments are repeated todeposit multiple layers.

More particularly and with reference to the figures, a semiconductorwafer is indicated generally by reference numeral 10, and comprises abulk substrate 12. Such would be positioned within a chemical vapordeposition reactor for processing in accordance with the invention. Anorganic precursor and typically a carrier gas would be injected towithin the reactor, and the reactor maintained at temperature andpressure conditions which, in combination, are effective to deposit athin first layer 14 (FIG. 2) of material onto the wafer. Undesirably,carbon from the organic precursor will be incorporated into thedeposited first layer.

As an example where the deposited layer is desired to be TiN, one typeof precursor would be organometallic precursors such as TDMAT. Anexample component and carrier gas would be N₂. For titanium nitride, thepreferred pressure is from 0.1 Torr to 10 Torr. The preferredtemperature is 200° C. to 700° C. A specific reduction to practiceexample temperature and pressure were a wafer carrier temperature of420° C., and a reactor pressure at 0.5 Torr. Titanium from theorganometallic precursor is intended to combine with the nitrogen todeposit a TiN layer. Undesirably, some of the carbon from the organicprecursor combines with the titanium to form TiC, as opposed to thedesired TiN. While the resultant film will still predominantly compriseTiN, 20 molar percent or greater TiC can be formed within the film.Further and even more undesirable, hydrocarbon products from theprecursor typically become incorporated in the film, further adverselyaffecting conductivity. Example thickness for layer 14 is from a singleatomic thick layer to 40 Angstroms, with about 15 Angstroms beingpreferred. Alternately, thicker layers such as 100 Angstroms or greatermight be utilized.

After depositing first layer 14, injection of the organic precursor isceased, and a first injection of a component gas into the reactor isconducted. Preferably, a time lag is provided between the ceasing ofinjection of the organic precursor and the injection of the componentgas, with an example and preferred time lag period being 5 seconds.Within the reactor, a first plasma is generated from the component gasagainst first layer 14. Advantageously, the substrate can be biased witha negative voltage (i.e., -100 Volts) during the plasma treatment toattract ions against the substrate. An example reduction-to-practiceplasma density of 10⁸ to 10⁹ ions/cm³ was utilized. High density plasma(i.e., 10¹² to 10¹³ ions/cm³) may also be employed to obtain a higherdensity of ions at lower process pressures. Such will facilitate ionbombardment as well as removal of carbon-containing reaction byproductsfrom the surface of the film.

In accordance with the parent patent application disclosure, thecomponent gas had to at least comprise hydrogen atoms and interact bychemical interaction. In accordance with this continuation-in-partdisclosure, the component gas does not necessarily comprise hydrogenatoms and does not require chemical interaction in the literal sense.Yet, the component gas need contain some component which is effectivewhen in an activated state to interact with a component of depositedfirst layer 14. In one preferred embodiment, this activated statecomponent effectively diffuses into the first layer and interacts withthe deposited first layer component to remove carbon from the firstlayer and produce gaseous products which are expelled from the reactor.Carbon incorporation in the resultant film is thus minimized. Also, thefirst layer component might comprise unbonded and incomplete electronshell carbon atoms. The activated state component in this example wouldchemically react with the unbonded and incomplete electron shell atomsto drive carbon from the film.

By way of example, the component gas might consist essentially of N₂. Ifthe deposited film comprises undesired TiC (and also perhapshydrocarbons) where the desired composition is TiN, the nitrogen plasmapresents a component (atomic or ionic nitrogen) against the depositedfilm. This component is chemically reactive with a component of thedeposited film (carbon) to remove or displace carbon from such film, andproduce gaseous products (i.e., CN compounds) which are expelled fromthe reactor. The goal or intent with this example is to provide a gaswhich has some chemically reactive component which breaks a bond withinthe deposited film to cause carbon (in any of atomic, radical, ormolecular radical form) to be displaced from the film and out of thereactor. The component from the gas might remain in the deposited film,combine with the displaced carbon and exit the reactor, or singularlyexit the reactor without combining with carbon or other material of thedeposited film. Also in this example, H₂ might be combined with the N₂gas.

In the above nitrogen example, atomic N functions as a non-metallicbonding component to the metallic Ti, and results in conductive TiN. Asanother alternative, the component gas might consist essentially ofhydrogen, or a combination of two or more reactive components. NH₃ is anexample of a single component and chemically reactive gas which canpresent multiple components (N atoms and H atoms) which are separatelyreactive with components of the example TiN deposited films. Some of theN atoms would become incorporated into the film in place of thedisplaced carbon, while the H atoms would most likely combine with thedisplaced carbon to form stabilized hydrocarbons which are predominatelyexpelled from the reactor. An example RF power range for plasmatreatment is from 50 to 1,000 W.

As an alternate example, the component gas might consist essentially ofelemental Ar. The interaction for carbon removal in this and the aboveexamples may be chemical, physical or a combination of both. The plasmaargon ions would bombard the deposited film and react or impinge uponunbonded and incomplete electron shell carbon atoms to effectively drivecarbon from the film. Carbon remaining deeper within the film would thenoutwardly diffuse to be impinged upon by more argon plasma, and bedisplaced from the film.

Other examples include CVD of Al₂ O₃ whereby the component gas wouldpreferably include O₂. Where the material being deposited is elementalmetal, the preferred component gas preferably includes H₂.

Also, the deposition to produce layer 14 could be conducted with orwithout plasma enhancement, while the reactive ion bombardment of thefirst reactive treatment will always involve plasma in accordance withthis invention.

After the first plasma treatment, the organic precursor is againinjected to within the reactor which is again maintained at atemperature and pressure which in combination are effective to deposit asubsequent second layer atop layer 14. Again, the outer layer willincorporate carbon from the organic precursor, and in the describedexample typically in the form of a carbide and hydrocarbons. FIG. 3illustrates layer 14 having grown to be twice its thickness as layer14a, with the outer portion of layer 14a constituting the seconddeposited layer. Carbon will be largely concentrated in this outerregion, having been previously removed from the underlying layer 14.

After deposition of this second layer, injection of the organicprecursor is ceased, and a second injecting of a component gas isconducted. A second plasma from the component gas within the reactor isgenerated to cause plasma ions to bombard against the second layer. Thesecond plasma will effectively will present a component which interactswith carbon of the carbide in the second layer, as well as entrainedhydrocarbons, to produce gaseous products which diffuse outwardly of thesecond layer and are expelled from the reactor. Such second plasmatreatment is preferably essentially identical to the first, andconducted at a considerably greater time than the time period for thedeposition of the second layer. Further preferably, a time lag isprovided between ceasing of the injection of the organic precursor andinjection of the component gas, with an example preferred time periodbeing 5 seconds.

Referring to FIG. 4, the alternating deposition and treatment sequencesare continued until a desired thickness layer 14z is produced.Accordingly, deposition is preferably pulsed with intervening plasmatreatment. Typically and most preferably, the sum of the plasmatreatment steps time periods will be at least two times the sum of theorganic precursor injection Steps time periods to facilitate carbonremoval from the desired deposited layer. Time for plasma treatmentswill be impacted by density and permeability of ions from the plasmainto the deposited films.

The invention also contemplates single layer deposition with one or moreplasma treatments thereof, as well as products produced by the aboveprocesses.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features described, since the means herein disclosedcomprise preferred forms of putting the invention into effect. Theinvention is, therefore, claimed in any of its forms or modificationswithin the proper scope of the appended claims appropriately interpretedin accordance with the doctrine of equivalents.

I claim:
 1. A chemical vapor deposition method comprising the following steps:injecting an organic precursor to within a reactor having a wafer positioned therein, and maintaining the reactor at a temperature and a pressure which in combination are effective to form a first layer on the wafer, the first layer comprising carbon in the form of a carbide; and after forming the first layer, ceasing to inject the organic precursor into the reactor and injecting a component gas into the reactor and generating a plasma from the component gas within the reactor, the component gas providing an activated component which is effective to remove carbon of the carbide from the first layer, the component gas providing a bonding component which replaces and substitutes for the carbon displaced from the carbide in the first layer.
 2. The chemical vapor deposition method of claim 1 wherein the activated state component effectively diffuses into the first layer and chemically reacts with a first layer component to remove carbon from the first layer.
 3. The chemical vapor deposition method of claim 1 wherein the component gas comprises N₂.
 4. The chemical vapor deposition method of claim 1 wherein the component gas comprises N₂ and H₂.
 5. The chemical vapor deposition method of claim 1 wherein the component gas comprises Ar.
 6. The chemical vapor deposition method of claim 1 wherein the component gas consists essentially of N₂.
 7. The chemical vapor deposition method of claim 1 wherein the component gas comprises NH₃.
 8. The chemical vapor deposition method of claim 1 further comprising biasing the substrate to a negative voltage during the plasma treatment.
 9. A chemical vapor deposition method comprising the following steps:injecting an organic precursor within a reactor having a wafer positioned therein, and maintaining the reactor at a temperature and a pressure which in combination are effective to form a first layer on the wafer, the first layer comprising carbon; after forming the first layer, ceasing to inject the organic precursor into the reactor and first injecting a component gas into the reactor and generating a first plasma within the reactor, the component gas consisting essentially of N₂, the component gas providing an activated component which is effective to remove carbon from the first layer; after the first plasma treatment, injecting the organic precursor to within the reactor having the wafer positioned therein, and maintaining the reactor at a temperature and a pressure which in combination are effective to form a second layer on the wafer, the second layer comprising carbon; and after forming the second layer, ceasing to inject the organic precursor into the reactor and second injecting the component gas into the reactor and generating a second plasma within the reactor, the component gas providing an activated component which is effective to remove carbon from the second layer.
 10. A chemical vapor deposition method comprising the following steps:injecting an organic precursor within a reactor having a wafer positioned therein, and maintaining the reactor at a temperature and a pressure which in combination are effective to form a first layer on the wafer, the first layer comprising carbon; after forming the first layer, ceasing to inject the organic precursor into the reactor and first injecting a component gas into the reactor and generating a first plasma within the reactor, the component gas comprising at least one of the elements N or Ar, the component gas providing an activated component which is effective to remove carbon from the first layer; after the first plasma treatment, injecting the organic precursor to within the reactor having the wafer positioned therein, and maintaining the reactor at a temperature and a pressure which in combination are effective to form a second layer on the wafer, the second layer comprising carbon; after forming the second layer, ceasing to inject the organic precursor into the reactor and second injecting the component gas into the reactor and generating a second plasma within the reactor, the component gas providing an activated component which is effective to remove carbon from the second layer; and wherein the organic precursor injection steps and the plasma treatment steps are conducted for respective time periods, the sum of the plasma treatment step's time periods being at least two times as great as the sum of the organic precursor injection step's time periods.
 11. A chemical vapor deposition method comprising the following steps:injecting an organic precursor within a reactor having a wafer positioned therein, and maintaining the reactor at a temperature and a pressure which in combination are effective to form a first layer on the wafer, the first layer comprising carbon in the form of a carbide; after forming the first layer, ceasing to inject the organic precursor into the reactor and first injecting a component gas into the reactor and generating a first plasma from the component gas within the reactor, the component gas providing an activated component which is effective to remove carbon of the carbide from the first layer, the component gas providing a bonding component which replaces and substitutes for the carbon displaced from the carbide in the first layer; after the first plasma treatment, injecting the organic precursor to within the reactor having the wafer positioned therein, and maintaining the reactor at a temperature and a pressure which in combination are effective to form a second layer on the wafer, the second layer comprising carbon in the form of a carbide; and after forming the second layer, ceasing to inject the organic precursor into the reactor and second injecting the component gas into the reactor and generating a second plasma from the component gas within the reactor, the component gas providing an activated component which is effective to remove carbon of the carbide from the second layer, the component gas providing a bonding component which replaces and substitutes for the carbon displaced from the carbide in the second layer.
 12. The chemical vapor deposition method of claim 11 wherein the activated state component effectively diffuses into the first layer and chemically reacts with a first layer component to remove carbon from the first layer and produce gaseous products, and wherein the activated state component effectively diffuses into the second layer and chemically reacts with a second layer component to remove carbon from the second layer and produce gaseous products.
 13. The chemical vapor deposition method of claim 11 wherein the component gas comprises N₂.
 14. The chemical vapor deposition method of claim 11 wherein the component gas comprises N₂ and H₂.
 15. The chemical vapor deposition method of claim 11 wherein the component gas comprises Ar.
 16. The chemical vapor deposition method of claim 11 wherein the component gas consists essentially of N₂.
 17. The chemical vapor deposition method of claim 11 wherein the component gas comprises NH₃.
 18. The chemical vapor deposition method of claim 11 further comprising biasing the substrate to a negative voltage during the first and second plasma treatments.
 19. The chemical vapor deposition method of claim 11 wherein each of the first and second layers are deposited to respective thicknesses of less than 50 Angstroms. 